Shuji Nakamura: New Materials Light The Way To Blue LED Innovations

Shuji Nakamura is one of 2013's inductees to Electronic Design's Hall of Fame. He successfully built on earlier efforts to create semiconductor diodes from III/V compounds with band gaps that would result in the emission of blue-light photons at the junction. combined with yellow-emitting phosphors inside the LED package, this results in what the eye perceives as "white" light. Replacing inefficient incandescent and flouresecnt light sources with efficient white LEDs has opened numerous energy-saving possibilities in applications as diverse as camera flashes and street ighting.

Shuji Nakamura enabled an entire industry based on high-brightness LEDs replacing incandescent, gas-discharge, and fluorescent lighting in vehicles, homes, businesses, and outdoors. He did it by developing a practical way to manufacture efficient blue and ultraviolet LEDs, which are the basis for “white” LEDs.

The challenge for LED lighting is that the wavelength of the light emitted is determined by the band gap of the semiconductor material from which the diode is fabricated. Red and green LEDs were fairly easy. But blue, which could be used with “yellow” phosphors to produce a mix of photons that would appear white, was another story (see “Understanding LED Application Theory And Practice” at electronicdesign.com).

Theoretically, some compound semiconductor materials from groups III and V of the old atomic table might be satisfactory. However, the process technologies needed to create them were yet to be uncovered. Building on decades of prior work, Nakamura unlocked the secret. (In today’s atomic table, groups III and V are now designated groups 13 and 15.)

Nakamura also is a hero to many working engineers for his legal actions to collect his fair share of profits that accrued to his employer from his invention. A Japanese court deemed an initial single royalty payment of the equivalent less then $200 in yen would more fairly have been on the order of $180 million. Ultimately, the parties settled on the equivalent of $8.1 million.1

Building On Earlier Work

Nakamura’s research didn’t take place in a vacuum. Previously, the hunt for an economically sustainable way to manufacture blue LEDs on silicon carbide (SiC), gallium phosphate (GaP), and gallium nitride (GaN) had been long and frustrating, with very disappointing electrical-to-optical conversion efficiencies.2

In the late 1960s and early 1970s, RCA came very close to developing viable blue LEDs, thanks to the research of James Tietjen, Jacques Pankove, Ed Miller, David Stevenson, and Maruska, working collaboratively at RCA Laboratories and Stanford University. When RCA went out of business in 1986, though, that research virtually stopped.

Meanwhile, in Japan in the late 1960s, Isamu Akasaki had begun working on GaN-based blue LEDs at Matsushita Research Institute. Then, in 1989 at Nagoya University, Akasaki developed the first GaN p-n junction blue/UV LED. The p-n junction was a major breakthrough.

As Nakamura Tells It

In a speech at the Takeda Award forum in 2002, Nakamura described his evolution from a young graduate engineer with a specialty in electronics to a semiconductor process researcher.3 In his first job after graduation at Nichia Corp., he researched GaP crystal growth heating compounds in quartz tubes. It was not ideal.

“I spent almost every day welding quartz tubes, inserting raw materials and heating them in the furnace, where they would explode with a loud bang,” he said. “I was just a quartz-welding technician at that time! I couldn’t imagine my present situation. At that time I thought that my whole life was over.”

Then he was asked to do development work on gallium arsenide (GaAs), which can be produced using a similar method. At this time, GaAs was used for red and infrared LEDs. After three years of that, he worked on the epitaxial growth of gallium aluminum arsenide (GaAlAs) and developed practical infrared and red LEDs.

But speaking perfectly frankly about the situation then, he said, “Unfortunately, the devices which were developed did not sell well, and so the company spoke badly of me. I was seen as a freeloader.”

Nevertheless, while he had been developing LEDs during those 10 years, he had always wanted to try and develop a blue LED. But the company feared that it lacked the resources to pursue that goal successfully.

“After completing my tenh year, I was urged to quit the company and so I blew a fuse. I decided to propose the development of blue LED, which I wanted to develop, and if it was impossible, then I would resign the company.”

Nakamura was surprised when company founder Nobuo Ogawa approved.

“I stuck my neck out and said, ‘We need a budget of several hundred million yen in order to complete the development of blue LED.’ He replied ‘okay.’ Then, I asked him to permit me to study abroad at Florida University for one year. Again, ‘okay.’ Everything was okay in just 5 seconds. It was that easy,” he said.

“I went abroad to Florida University where I wanted to study MOCVD (metal organic chemical vapor deposition), and on my return I started practically the research of blue LEDs,” he said.

Nakamura notes that the price of the MOCVD equipment was 2 hundred million yen, which made him feel pressure to get some results. “So I began to modify the equipment in my own way. I continued making these modifications every day for one-and-a-half years,” he said.

In the summer of 1990, he invented Two-Flow MOCVD. “When I used this to grow GaN crystals, I could get results superior to the data of what had been the best in the world up until then. I was absolutely delighted,” he said.

Using the modified equipment, he made crystals one after the other. Over two to three months, he produced several “first in the world” and “best in the world” results, such as indium gallium nitride (InGaN).

He also experimented with modifying the structure of the LED devices. “I could get an extremely bright light,” he said. He made other breakthroughs, including obtaining p-type GaN. “I had succeeded in getting p-type GaN simply by heat treatment,” he said. “Once again it was the quality of the equipment that had allowed me to produce such high quality p-type GaN.”

This was in the summer of 1990. That work resulted in a blue LED that emitted strong light in a laser diode.

Secrecy And Patents

Ironically, considering the patent issues that would later evolve, this activity almost did not result in patents.

“The company prohibited publishing articles and speaking at academic conferences. Even applications for patent types that were subject to public disclosure were prohibited. All patent applications were limited to ‘know-how’ applications (not made public by the patent office),” Nakamura said.

However Nakamura had felt humiliated when he first arrived at the university in Florida. He felt that the other grad students did not respect him because he had not published as they had. He decided he was not going to put up with that disrespect any more.

“After I succeeded with Two-Flow MOCVD, I submitted the articles in secret. Before submitting the articles, I made patent applications as a way of covering my back once the articles were publicized,” he said.

“I succeeded in commercializing the blue LED in 1993. This device emitted bright light with intensity more than 100 times brighter than previous devices. I also developed and announced the commercialization of green LEDs in 1995. I achieved the first laser oscillation in late 1995 and succeeded in the commercialization of the blue laser in about 1999. In the meantime I made several hundred patent applications and about 50 important patents were granted that produced profits for the company,” he said.

In 1999, after he was moved into management, a job that he hated and called “stamping papers,” Nakamura decided to leave the business world for the academy and joined the faculty at the University of California, Santa Barbara.

At Court

For Japanese engineers, the decision is considered a landmark. According to TheNew York Times, the case was closely watched in Japan as a test of long-held notions that employees should sacrifice everything for their companies and that there was something unseemly about individual workers, even the most productive ones, seeking a bigger cut of profits than their coworkers.

Traditionally, corporate engineers and scientists in Japan were treated just like less skilled employees, the Times explained. Unlike American companies, Japanese companies seldom signed contracts with their researchers specifying how profits from their inventions will be shared.

The Resume

Shuji Nakamura was born in 1954 in Ehime, Japan. He obtained BE, MS, and PhD degrees in electrical engineering from the University of Tokushima, Japan, in 1977, 1979, and 1994, respectively. He joined Nichia Chemical Industries Ltd in 1979. In 1988, he spent a year at the University of Florida as a visiting research associate.

He is also the founder of Soraa, the only company making commercial GaN-on-GaN LED lighting products. According to the company, GaN-on-GaN LED material supports very high current densities because it has 1000 times fewer lattice defects than LEDs in which the epitaxial GaN layers are grown on less expensive sapphire, SiC, or silicon substrates. With fewer lattice defects, the Soraa LEDs emit 10 times more light per unit area of LED material than conventional LEDs.